The principal commercial surfactants in use today are linear alkylbenzene sulfonates and linear alcohol ethoxylates. The hydrophobic portion of both surfactants is a linear alkyl chain of between eleven and eighteen carbon atoms. These surfactants had been preceded by synthetic detergents which contain highly branched groups as a hydrophobic portion. The change to the currently employed linear groups, which occurred in the 1960's, was prompted by concern over the slow biodegradation characteristics of the branched hydrophobes. The perceived need for linearity led to development of particular approaches to hydrophobe preparation. The linear alkyl benzene sulfonates are based upon linear olefins derived from paraffins, which in turn are obtained through molecular sieve separations from paraffin mixtures. The linear alcohol based detergents are produced by way of ethylene oligomerization, followed by processes to manipulate the broad range of olefins obtained into the desired molecular weight range. The processing involved in such approaches adds considerably to energy and facilities usage and consequently to product cost. When olefins of the requisite carbon atom number have been obtained, they can be hydroformylated to produce aldehydes, generally with one more carbon atom than the olefin, which can be hydrogenated to an alcohol.
An alternate method for generating longer chain alcohols from short chain olefins is via a sequence involving hydroformylation (or oxo reaction) followed by aldol condensation and hydrogenation. Thus 2-ethylhexanol is prepared on a very large scale by (a) hydroformylating propylene to a mixture of n-butanal and isobutanal, (b) separating the mixtures of aldehydes (c) aldol reaction of n-butanal to 2-ethylhexenal and (d) hydrogenation of 2-ethylhexenal to 2-ethylhexanol. While this approach is well-recognized to be cost effective for generation of medium chain alcohols, it has not heretofore been shown to be an economical method for generation of longer chain alcohols. Among patents teaching conversion of aldehydes to higher aldehydes by the well known aldol reaction is U.S. Pat. No. 2,852,563.
Medium chain length olefins are usually derived from dimerization or oligomerization of ethylene or propylene. Among dimerization processes is the Dimersol.RTM. dimerization process for dimerizing olefins using a nickel coordination complex and an aluminum alkyl as catalyst. The process can convert propylene to hexenes with selectivity in excess of 85%. The hexanes can be converted by oxo reaction to aldehydes and then alcohols, producing heptanols. Processes are also known for dimerizing propylene with trialkylalumminum metals to 4-methyl-1-pentene, see Industrial Organic Chemistry, Klaus Weissermel and Hans-Jurgen Arpe; English translation by Alexander Muller (Verlag Chemie, Weinheim, New York, 1978), pp 75-77. Also oxo reactions of certain branched olefins have been studied, see M. Johnson, Chem. Soc. 1963, 4859; Piacenti et al, J. Chem. Soc., 1966, 488; and Vysokinskii et al, J. Applied Chemistry of USSR, 1972, Vol. 45, pp. 1352-1355. Also oxo reactions of certain non-terminal octenes have been reported to give less than 60% of the straight chain aldehyde isomers, see Kummer et al, Homogeneous Catalysis-II, pages 19 to 26, Advances in Chemistry Series 132 (Edited by Denis Forster and James F. Roth), American Chemical Society, Washington D.C., 1974.
Reactions of the type described characteristically produce mixtures of products, often with extensive branching. Therefore, in order to control the branching, or to eliminate unreactive components, it has been common practice to employ distillation at intermediate stages to remove some of the isomer.